Automotive vehicles include sprung and unsprung masses, wherein, for a vehicle with body and frame, the sprung mass includes the vehicle's frame and body that is fixed to the frame, while the unsprung mass includes the wheels and portions of the vehicle's suspension connecting the sprung mass to axles for the wheels. The sprung mass for vehicles with structurally indistinguishable bodies and frames, referred to as unibody construction, is the total mass of this combined structure; the sprung mass for this type of vehicle is identical to that of the body and frame vehicle. Typically, the sprung mass is connected to wheel axles by shock absorbing devices which include soft springs allowing relative motion between the sprung and unsprung masses and dampers which primarily limit repetitive cyclic motions of the unsprung and sprung masses. Although the damping devices can employ one of many energy-dissipative alternatives and actuations, such as pneumatic or electric, the dominant configuration is hydraulic.
Typically, these fluid filled dampers comprise a hydraulic cylinder with a piston therein that throttles a fluid flow from one side of the piston to the other through apertures in the piston. Currently, there are attempts to increase vehicle ride comfort in at least some vehicles by programmatically regulating damping forces. One such approach involves continually adjustable effective orifice size to preferably regulate the resistance to fluid flow so that damper performance corresponds to desirable performance for the particular operating conditions of the vehicle. These operating conditions change instantaneously depending on vehicle usage, such as on rough roads, smooth roads, during cornering and the like. These programmable devices, employing sensing, control means, and attendant hardware also provide the intended multiple stage performance, but offer a more expensive mechanization to achieve the desired effect. Another suggested approach involves electro-rheological fluid or magnetic-rheological fluid with sensing and control means to adjust flow resistance. Such arrangements are, like the variable orifice size mechanization, complex and relatively expensive.